Chelating agents are molecules that form two or more coordinated covalent bonds to a metal ion and are also classified as sequestering agents. The most commonly used chelating agents are those that coordinate to a central metal ion through oxygen, nitrogen, or a combination of oxygen and nitrogen donor atoms yielding the respective inorganic coordination compound. Chelating or sequestering agents typically form water-soluble metal complexes and therefore are very useful in various industrial and commercial applications including pulp and paper manufacturing, metalworking and metal plating, pharmaceuticals, water treatment, textile manufacturing and dyeing, agriculture, cleaning and detergent formulations, and food processing. Chelating or sequestering agents may be used in the aforementioned applications alone or with surfactants, builders or other chelating agents.
A major concern surrounding chelating agents is environmental accumulation as a result of persistence meaning the inability to biodegrade under environmental conditions. For example, ethylenediaminetetracetic acid (EDTA), a preferred chelating agent due to its low cost and high metal binding affinity over a large pH range has been scrutinized because of its environmental persistence. Elevated concentrations of EDTA and other nonbiodegradable chelating agents pose major environmental concerns such as heavy metal remobilization and plant (e.g. algae) growth alteration. As a result, many processes and methods have been reported for the preparation of biodegradable chelating agents.
Current methods have focused on the use of sustainable and/or renewable feedstocks to produce biodegradable chelating agents. However, a commonly utilized process for the industrial preparation of many chelating agents involves the use of cyanide, formaldehyde and sodium hydroxide resulting in nitrilotriacetic acid (NTA) contamination. While NTA is biodegradable, it is not preferred from the point of environmental health because it has been reported that NTA has teratogenicity and nitrilotriacetic acid-iron complex has carcinogenicity. Among other conventional carboxylated amines, those that are excellent in chelating performance, but are low in biodegradability have the difficulty that they accumulate as injurious heavy metals in the environment when they are discharged into the environment. Other processes for synthesizing carboxylated amines are disadvantageous due to high salt concentrations; for example, they contain high sodium chloride concentrations that can only be removed through tedious purification steps (i.e. ion exchange).
Accordingly, a need exists for another method for preparing chelating or sequestering agents. Disclosed is a method for synthesizing biodegradable chelating agents free of NTA with miniscule concentration of salt byproducts that minimizes production cost and avoids undesirable byproduct contamination.